Lens shading (also known as vignetting) is an optical effect that occurs when less light penetrates through the periphery of a lens than through the center. Lens shading causes corners of an image to become darker than the center of the image.
Color shading occurs when the shading of different color channels is different. Color shading results in unbalanced colors towards the periphery of the image. This effect may be found in most imaging systems, but becomes more substantial as image sensor size (or pixel size) decreases.
Effects of color shading usually accompany lens shading. Thus, conventional anti-shading correction methods only target lens shading correction directly. As a result, conventional anti-shading correction methods correct color shading and lens shading together, rather than separate and independently.